Devices

catarinamarcolin 3:18 pm on February 25, 2016

Laser Optical Particle Counter: LOPC

In Brazil we have the model LOPC660. It is mounted on a T-frame with an interoperable Micro-CTD (AML Microsystems).

— min and max particle size that can be captured:
0.1 to 35 mm

— volume of water that is captured:
The sampling tunnel area is 70 x 70 mm, and the beam area (frontal cross-section) is 49 cm2.

— raw output format:
*.dat and *.bin (I explain very briefly what informations are provided in the .dat file in my thesis. If someone is curious to get the basics I can send it by email, couldn’t find the way to attach it here).

— level of identification:
Particles. There are available techniques to separate out what is believed to describe marine snow and what is believe to describe zooplankton (see Jackson and Checkley 2011; Petrik et al., 2013).

— deployment details (towed, vertically lowered, on autonomous platform, etc):
Towed. We usually perform vertical tows.

— deployment restrictions:
Power consumption.

— need for calibration –> It’s calibration is made under dry conditions in the laboratory with three sizes of beads provided by the manufacturer.

ZooScan

The ZooScan provides digital images from preserved plankton samples.

— min and max particle size that can be captured:
0.3 to ~35 mm

— volume of water that is captured:
Typically, you can scan a fraction of a preserved plankton net sample.

— raw output format:
*.pid –> a data file resulting from image analysis by ZooProcess, each row represents a particle/organism and the variables associated to it.
*.jpg –> vignettes in *.jpg are images of single detected particle/organisms.
*.txt –> after validation it provides a text file with the classification of each particle/organism and its associated variables (e.g., area, length, ESD).

— level of identification:
Particles that were not disrupted by nets and zooplankton (variable taxonomic resolution).

— deployment details (towed, vertically lowered, on autonomous platform, etc):
Cannot be deployed, it is a benchtop device.

— need for calibration
“ZooScans can be calibrated so that different ZooScan units produce normalized images of identical optical characteristics” (Gorsky et al., 2010).
natetb 4:16 pm on March 10, 2016

Optical Backscattering Sensor (WET Labs ECO puck)

– min and max particle size that can be captured
~1 µm to ~1 mm

– volume of water that is captured:
~0.6 ml (N. T. Briggs et al. 2013)

– raw output format (e.g. image as .jpg, etc.)
Text files containing timeseries.

– level of identification; e.g. broad categories (particle, zooplankton), fine identification (down to genus level)
Information about individual particles is limited. The instrument only returns bulk particle backscattering (a proxy for particle concentration). Multiple measurements are required to obtain some particle size information from high frequency fluctuations of concentrations within the sample volume. At high particle concentrations, we can obtain bulk particle concentration along with a single estimate of mean particle size for these particles (N. T. Briggs et al. 2013).

At low particle concentrations (e.g. mesopelagic), we can obtain concentrations for two different size classes (N. Briggs et al. 2011). Very roughly, the two classes are small (100µm). The exact threshold depends on platform movement speed and instrument noise, and the threshold itself has some leakiness (some large particles will register as small and vice versa). With the addition of an integrated chlorophyll a fluorometer, chlorophyll-containing particles, such as aggregates containing live phytoplankton, can be distinguished from fecal pellets and/or detrital aggregates. With the addition of a beam transmissometer, we gain some information about the refractive index of the particles (related to mineral vs organic content). Multiple wavelengths of optical backscattering provide some further information on particle composition, possibly related to particle size

– deployment details (towed, vertically lowered, on autonomous platform, etc)
Can be deployed on nearly any platform, including low-power autonomous floats and gliders.

– deployment restrictions (depth? temperature?)
Different depth ratings are possible, including 600 m and 2000 m

– power consumption
Low: 60 mA at 7-15 V

– need for calibration
Instruments are factory calibrated in units of backscattering. In situ dark profiles are recommended (sensor covered with black tape) as dark counts can differ from factory calibration. The units of backscattering can be converted to units of carbon or cross sectional area using empirical relationships, although uncertainty can exceed a factor of 2 without local calibration.

References:

Briggs, Nathan, Mary Jane Perry, Ivona Cetinić, Craig Lee, Eric D’Asaro, Amanda M. Gray, and Eric Rehm. 2011. “High-Resolution Observations of Aggregate Flux during a Sub-Polar North Atlantic Spring Bloom.” Deep Sea Research Part I: Oceanographic Research Papers 58 (10): 1031–39. doi:10.1016/j.dsr.2011.07.007.

Briggs, Nathan T, Wayne H Slade, Emmanuel Boss, and Mary Jane Perry. 2013. “Method for Estimating Mean Particle Size from High-Frequency Fluctuations in Beam Attenuation or Scattering Measurements.” Applied Optics 52 (27): 6710–25.
Klas 12:45 pm on July 4, 2016

Video Plankton Recorder (VPR)

The Video Plankton Recorder is an optical sampling gear and like an underwater microscope that is towed behind a research vessel. The VPR images plankton and particles within a size range of 50 microns to several millimeters at up to 25 frames per second along the tow-track. It can be chosen between four different calibrated magnifications with a sampling volume between 1 ml and several hundred ml depending on the depth of field. At the same time this instrument measures the physical environment (e.g. temperature, salinity and chlorophyll) in which these organisms are living and interacting with. Traditionally, net sampling was used to understand the distribution of planktonic organisms. However, due to the fragile nature of many of these organisms they are often destroyed when using plankton nets to collect them. Using this optical method allows to better assess the abundance and distribution of these fragile organisms and thereby gives new insights into plankton ecology and their role in the global carbon cycle.

We have several different VPR systems at the University of Hamburg:

Digital Autonomous VPR (DAVPR)

It is totally self-contained and can also be deployed from smaller Vessels. It is powered with batteries for app. 2 hours of continuos operation and images are stored to an internal harddrive. Additionally, it is equipped with a CTD for hydrographic information. Images are taken with 15 frames per second and it has a depth rating of 1000m.

Video Plankton Recorder II (real time system)

This VPR can be mounted below a depressor v-fin or attached to the high-speed towbody TRIAXUS (including a suite of different sensors as well as a LOPC)

It has a fibre-optic towcable and sends images and sensor data with 25 frames per second in real time to the deck computers on board. Due to this it needs its own winch with a fibre optic tow cable and, hence, can only be used from larger research vessels.

Stationary Video Plankton Recorder

A stationary underwater VPR in combination with an ADCP which has a data and power connection to the shore.

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TOMCAT | Translation of Optical Measurements into particle Content, Aggregation & Transfer | SCOR working group 150

SCOR Working Group 150 takes advantage of optical technologies to better understand the ocean carbon cycle: particle flux and zooplankton-particle interaction.

Devices